Until recently, pitot, static and total temperature probes have been the primary means of obtaining flow information in high speed flows. These probes have proven to be inadequate, however, for obtaining detailed measurements of more complex flow fields such as three-dimensional flows. As research in this area has heightened, so has the need for a means of accurately evaluating these flows. This increased need has been the primary impetus behind the development of nonintrusive measuring techniques.
One such technique, known as laser velocimetry, is designed to measure static density, temperature and three components of velocity in the flow field. The velocimeter is actually a particle velocity measuring device which requires the use of seeding particles in the flow to act as light scatters. It, therefore, will measure the gas velocity only if the particle and gas velocities are the same. Consequently, the particle requirements of this system are an important factor in its successful operation. Initially, there must be a sufficient number of particles of uniform size to obtain a statistically reliable velocity average at a point. The particles must be small and low in density to follow the flow, but they must be large enough to scatter light sufficient for the receiving optics to measure. In addition, the particles should not combust or evaporate in the high temperature and pressure of the setting chamber, and they should be both nonabrasive and noncorrosive.
This invention relates to a particle generating system which is capable of breaking up agglomerations of particles and producing a cloud of uniform, submicron-sized particles at high pressure and high flow rates. Conventional particle generators are incapable of meeting the rigorous demands imposed by the laser velocimeter. Smoke generators, although commonly used in other settings, are nonfunctional at the high mass flow rates (higher densities) and high pressure of the velocimeter's hypersonic tunnel because of the resultant interference with the generator's evaporation and condensation processes. In addition, such systems are very sensitive to small changes in the stagnation pressure of the tunnel. Fluidized bed systems are also inadequate because of their tendency to produce only aggregates or agglomerates of particles rather than single particles. This invention was designed to overcome the deficiencies of these previously utilized systems.
Accordingly, it is an object of this invention to provide an apparatus which is capable of producing a cloud of uniform, submicron-sized particles at high pressure and high flow rates.
Another object of the invention is to provide a particle generating system which remains independent of external environmental conditions.
Another object of the invention is to provide an apparatus which will effectuate consistent and uniform separation of particle agglomerations.